Antibiotics during pregnancy may affect a child's behaviour

Taking antibiotics during pregnancy may lead to behaviour changes in your child.
11 April 2017

Interview with 

Dr John Bienenstock, McMaster University


Tablets and capsules


Penicillin has saved millions of lives since its antibacterial properties were realised in patients in 1942. Now, literally thousands of tonnes of antibiotics like penicillin get used every year around the world. But could there be consequences for a developing baby’s brain if its mother takes antibiotics during her pregnancy? New research from Canada, carried out on mice, suggests that taking antibiotics changes the spectrum of bugs in the mother’s - and subsequently the infant’s - intestines. John Bienenstock told Chris Smith how this might affect brain chemistry and the behaviour of the infant after it is born...

John - We postulated an antibiotic might change the balance of bacteria in the gut. If we gave it, in pregnancy, and then continued until the animals separated and were independent from their mothers, would there be a change in brain activity or behaviour? And the short answer is yes - animals became aggressive, quite unusually, and there were chemical changes in the brain. These are associated with the changes in the bacteria in the gut.

Chris - How do you know, though, that the differences you’re seeing are not just a side effect of the antibiotic molecule?

John - What we did was to give another group that were receiving antibiotics a bacterium commonly referred to as a "probiotic", and when we did that we found that there was a marked difference. The effects were not so significant or concerning in the brain and in terms of behaviour, and the changes that we saw in the bacteria in the gut, which were drastically altered by the antibiotic, were actually not seen. So we take this as demonstrating that the bacteria may well be significantly involved in the causation of the abnormalities.

Chris - If you look in the brains of the mice that you have treated in this way and seen these changes and behaviour, are there any obvious differences that would account for why they’re behaving differently?

John - Yes. When we do, we find particular changes, which are quite dramatic, in the frontal cortex which is part of the brain that tends to regulate emotions and reactions in that sense. Those changes are associated with a particular molecule or receptor which has been shown to be associated with aggression, so our thought is that those are, in fact, associated with these behavioural changes.

Chris - Is this potentially then irreversible? Are the mice - once they’re like this - are they locked into this altered behavioural state?

John - We don’t know the answer to that. It’s a key question because, obviously, what we’re talking about is the difference between prevention and treatment. In addition, we don’t know whether the effects that we see are only related to pregnancy or whether, in fact, separating the experiments into two halves, one in which we treat animals with antibiotic in pregnancy and another which treats only the pups and then looks at the long term at offspring, which one of these is going to have that effect. We suspect that the results will be that the effect of the antibiotic is in pregnancy.

Chris - To what extent do you think that - because this is a study in mice isn’t it - what extent do you think this is relevant to humans?

John - It’s the most important question. In North America, currently, the statistics show that every child by the age of two receives one or two courses of antibiotic. That doesn’t mean to say that the antibiotic isn’t necessary - it’s just a fact. We know very little about the incidence of psychiatric disease, at least the risk for the development of psychiatric disease, as a result of  antibiotics. We do know that antibiotics are associated with several different clinical diseases such as inflammatory bowel disease, colon cancer and also, interestingly enough, obesity. But we do not know whether antibiotics in pregnancy have any affect at all, so the epidemiological evidence will be some time in the coming to either prove or disprove the current results in mice.


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